1. Field of the Invention
The field of the invention is data processing, or, more specifically, methods and products for a printed circuit board (PCB) with reduced dielectric loss.
2. Description of Related Art
Dielectric loss is one of the main reasons for AC signal loss in PCB channels. Electronic signaling speed is bound by the noise and loss in the communication channel. While noise can be contained by careful design, inherent electromagnetic properties of conductors such as dielectric loss reduces the energy of the transmitted signal causing distortion and difficulty in recovering the information transmitted.
Most dielectrics are imperfect conductors of AC signals; they present a form of resistance that causes signal loss. The tendency of a dielectric to cause such ‘dielectric loss’ is quantified by various measures, including, for example, dielectric constant, relative dielectric constant, various measures of permittivity such as ‘relative static permittivity’, the ‘attenuation constant,’ the ‘loss tangent,’ and so on. The least lossy dielectric is a vacuum, with a dielectric constant of 1.0. Typical relative dielectric constants, that is, ‘relative’ to the dielectric constant of a vacuum, for the dielectric laminate substrates used in PCBs, various combinations of woven glass and epoxy, for example, range roughly from 2-6. The most common dielectric today, FR4 typically demonstrates a relative dielectric constant of about 4.5.
A vacuum obviously is the preferred dielectric, but building PCBs with vacuum dielectric layers, is impractical. Other current approaches to the problem of dielectric loss include various methods of equalization such as transmitter side equalization, channel equalization, and receiver equalization. All these approaches, while effective, also require costly additional circuitry at the driver or receiver end. Other approaches that most high speed system designers take is to resort to a low loss material like IS-620 or Megtron 6. Low loss materials are usually 4-6 times more expensive than the standard dielectric material, FR4.